1、 GUIDANCE NOTES ON SPECTRAL-BASED FATIGUE ANALYSIS FOR VESSELS (FOR THE SFA (years) CLASSIFICATION NOTATION) JANUARY 2004 Guide to Color Coding Used in Online Version of the Guidance Notes The following summarizes the colors corresponding to Rule Changes, Corrigenda items and editorial changes in th
2、e Rules files which are available for download. Rule Changes: NOTICE NO. 1 August 2006 (effective 15 August 2006) NOTICE NO. 2 December 2007 (effective 1 December 2007) NOTICE NO. 3 November 2009 (effective 15 November 2009) NOTICE NO. 4 January 2012 (effective 1 February 2012) Corrigenda: CORRIGEND
3、A/EDITORIALS 14 July 2008 CORRIGENDA/EDITORIALS 9 July 2009 CORRIGENDA/EDITORIALS 1 February 2012 Editorials: Editorial Changes Guidance Notes on Spectral-Based Fatigue Analysis for Vessels GUIDANCE NOTES ON SPECTRAL-BASED FATIGUE ANALYSIS FOR VESSELS (FOR THE SFA (years) CLASSIFICATION NOTATION) JA
4、NUARY 2004 (Updated February 2012 see next page) American Bureau of Shipping Incorporated by Act of Legislature of the State of New York 1862 Copyright 2004 American Bureau of Shipping ABS Plaza 16855 Northchase Drive Houston, TX 77060 USA Updates February 2012 consolidation includes: November 2009
5、version plus Notice No. 4 and Corrigenda/Editorials. November 2009 consolidation includes: July 2009 version plus Notice No. 3. July 2009 consolidation includes: July 2008 version plus Corrigenda/Editorials. July 2008 consolidation includes: December 2007 version plus Corrigenda/Editorials. December
6、 2007 consolidation includes: August 2006 Notice No. 1 December 2007 Notice No. 2 ABSGUIDANCE NOTES ON SPECTRAL-BASED FATIGUE ANALYSIS FOR VESSELS .2004 iii Foreword Foreword This Guide provides information about the optional classification notation, Spectral Fatigue Analysis SFA (years) which is av
7、ailable to qualifying vessels as described in 1-1-3/20 of the ABS Rules for Building and Classing Steel Vessels, referred to herein as the Steel Vessel Rules. This guidance document is referred to herein as “this Guide” and its issue date is January 2004. Users of this Guide are encouraged to contac
8、t ABS with any questions or comments concerning this Guide. Users are advised to check with ABS to ensure that this version of the Guide is current. iv ABSGUIDANCE NOTES ON SPECTRAL-BASED FATIGUE ANALYSIS FOR VESSELS .2004 Table of Contents GUIDANCE NOTES ON SPECTRAL-BASED FATIGUE ANALYSIS FOR VESSE
9、LS CONTENTS SECTION 1 Introduction 1 1 Purpose and Applicability1 3 Background.1 5 Areas for Fatigue Strength Evaluation2 7 Detailed Contents of this Guide 2 FIGURE 1 Schematic Spectral-based Fatigue Analysis Procedure.4 SECTION 2 Establishing Fatigue Demand . 5 1 Introduction .5 3 Stress Range Tran
10、sfer Function.5 5 Base Vessel Loading Conditions 5 7 Combined Fatigue from Multiple Base Vessel Loading Conditions .6 SECTION 3 Environmental Conditions. 7 1 General .7 SECTION 4 Motion Analysis and Wave-induced Loads 8 1 General .8 3 Initial Balance Check 8 5 Essential Features of Spectral-based An
11、alysis of Motion and Wave Load9 5.1 General Modeling Considerations9 5.3 Diffraction-Radiation Methods .9 SECTION 5 Wave-induced Load Components. 10 1 General .10 3 External Pressure Component10 3.1 Total Hydrodynamic Pressures10 3.3 Intermittent Wetting10 3.5 Pressure Distribution on Finite Element
12、 Models 10 ABSGUIDANCE NOTES ON SPECTRAL-BASED FATIGUE ANALYSIS FOR VESSELS .2004 v 5 Internal Load Components11 5.1 Tank Pressures .11 5.3 Dry Bulk Cargo Loads .11 5.5 Container Loads 15 7 Loads from the Motions of Discrete Masses.17 FIGURE 1 Hold Boundary Definition 11 FIGURE 2 Vertical and Horizo
13、ntal Force Components of Quasi-Static Load 12 FIGURE 3 Normal and Tangential Load Components of Quasi-Static Load in a Rolled Position 13 FIGURE 4 Pressures Due to Vertical Acceleration 14 FIGURE 5 Pressures Due to Transverse Acceleration 15 FIGURE 6 Vertical and Transverse Force Components of Stati
14、c Load 16 FIGURE 7 Inertial Loads Due to Acceleration17 SECTION 6 Loading for Global Finite Element Method (FEM) Structural Analysis Model . 19 1 General .19 3 Number of Load Cases.19 5 Equilibrium Check.19 SECTION 7 Structural Modeling and Analysis 20 1 General .20 3 3-D Global Analysis Modeling.20
15、 5 Analyses of Local Structure 20 7 Hot Spot Stress Concentration .21 FIGURE 1 Definition of Hot Spot Stress.21 SECTION 8 Fatigue Strength. 22 1 General .22 3 S-N Data .22 SECTION 9 Fatigue Life (Damage) Calculation and Acceptance Criteria 24 1 General .24 3 Acceptance Criteria.24 APPENDIX 1 Wave Da
16、ta. 25 TABLE 1 ABS Wave Scatter Diagram for Unrestricted Service Classification.25 vi ABSGUIDANCE NOTES ON SPECTRAL-BASED FATIGUE ANALYSIS FOR VESSELS .2004 APPENDIX 2 Basic Design S-N Curves. 26 FIGURE 1 S-N Curves26 TABLE 1 Parameters For Basic S-N Design Curves .27 APPENDIX 3 Outline of a Closed
17、Form Spectral-based Fatigue Analysis Procedure 28 1 General .28 3 Key Steps in Closed Form Damage Calculation.28 5 Closed Form Damage Expression31 ABSGUIDANCE NOTES ON SPECTRAL-BASED FATIGUE ANALYSIS FOR VESSELS .2004 1 Section 1: Introduction SECTION 1 Introduction 1 Purpose and Applicability (1 De
18、cember 2007) Part 5C of the ABS Rules for Building and Classing Steel Vessels (Steel Vessel Rules) presents the simplified fatigue assessment criteria for the classification of the various types of specialized vessels covered by the Rules. A brief description of the background and objectives for the
19、se fatigue criteria is given in Subsection 1/3, below. In addition to the simplified fatigue strength criteria for ABSs classification purposes, the Owner may wish to apply more extensive Spectral-based Fatigue Analysis (SFA) techniques to the vessels structural systems. It may be an added objective
20、 of these Spectral-based Fatigue Analyses to demonstrate longer target fatigue lives than those minimally required for the classification of a vessel. The term, “more extensively,” means that the Spectral-based Fatigue Analysis technique, rather than the SafeHull Fatigue Assessment technique, a Perm
21、issible Stress Range method (see Subsection 1/3 below), is used to verify the adequacy of the fatigue lives of the critical locations in the structural system. The SafeHull Fatigue Assessment technique is still to be employed in the overall design and analysis effort for the structure. The results o
22、f the fatigue assessment should be used in the selection of areas for which the Spectral-based Fatigue Analyses will be done. ABS is to be consulted and is to agree on the structural locations that are to be subjected to the Spectral-based Fatigue Analysis. In recognition of the appropriate, additio
23、nal use of Spectral-based Fatigue Analysis, ABS will grant the optional classification notation, SFA (year). The SFA (year) notation means that the design fatigue life value is equal to 20 years or greater. The value in the parentheses is the design fatigue life equal to 20 years or more (in 5-year
24、increments), as specified by the applicant. It should be understood that only one, minimum designated life value is applied to the entire structural system. The fatigue life value refers to the target value set by the designer and not the value calculated in the analysis. The calculated values are u
25、sually much higher than the target values specified for design. For vessels complying with Part 5A “Common Structural Rules for Double Hull Tankers” or Part 5B “Common Structural Rules for or Bulk Carriers” of the ABS Rules for Building and Classing Steel Vessels, the design target fatigue life for
26、Spectral-based Fatigue Analysis is equal to 25 years. 3 Background In the Steel Vessel Rules applied to a vessel, design and analysis for fatigue strength is usually accomplished through a combination of methods. Designers commonly make primary use of what is referred to as the SafeHull “Fatigue Ass
27、essment” technique (e.g., for an oil tanker with length greater than 150 m: Steel Vessel Rules Appendix 5C-1-A1). This is a “designer-oriented”, permissible stress range approach that is readily applied to a large portion of the fatigue-critical structural details of a vessels hull structure. This t
28、echnique was derived by considering “unrestricted ocean service” environmental loadings (due to waves) and a design target fatigue life of 20 years. Section 1 Introduction 2 ABSGUIDANCE NOTES ON SPECTRAL-BASED FATIGUE ANALYSIS FOR VESSELS .2004 The Steel Vessel Rules do not preclude the imposition o
29、f requirements by ABS to demonstrate the adequacy of fatigue strength of structural components by additional or other techniques that include the Spectral-based Fatigue Analysis methods. Indeed, it is commonly necessary to perform Spectral-based Fatigue Analysis of structural details, which is beyon
30、d the range of applicability of the permissible stress range fatigue assessment approach. Furthermore, the vessel owner or designer is free to increase the target fatigue lives of some or all of the structural components above the 20-year minimum value, which is recognized by the optional classifica
31、tion notation, FL (years), in the Steel Vessel Rules and other ABS classification standards. Therefore, the incidental or supplementary use of Spectral-based Fatigue Analysis methods is not a reason to grant the SFA (years) notation. 5 Areas for Fatigue Strength Evaluation Reference should be made t
32、o the Steel Vessel Rules for specific “Guidance on Locations” that should be included in the fatigue assessment. 7 Detailed Contents of this Guide Spectral-based Fatigue Analysis is a complex and numerically-intensive technique. As such, there is more than one variant of the method that can be valid
33、ly applied in a particular case. ABS does not wish to preclude the use of any valid variant of a Spectral-based Fatigue Analysis method by “over specifying” the elements of an approach. However, there is a need to be clear about the basic minimum assumptions that are to be the basis of the method em
34、ployed, and some of the key details that are to be incorporated in the method to produce results that will be acceptable to ABS. For this reason, most of the remainder of this Guide is a presentation on these topics. As for the main assumptions underlying the Spectral-Based Fatigue Analysis method,
35、these are as follows. i) Ocean waves are the source of the fatigue inducing stress range acting on the structural system being analyzed. ii) In order for the frequency domain formulation and the associated probabilistically based analysis to be valid, load analysis and the associated structural anal
36、ysis are assumed to be linear. Hence, scaling and superposition of stress range transfer functions from unit amplitude waves are considered valid. iii) Non-linearities, brought about by non-linear roll motions and intermittent application of loads such as wetting of the side shell in the splash zone
37、, are treated by correction factors. iv) Structural dynamic amplification, transient loads and effects such as springing are insignificant in the typical case, hence, use of quasi-static finite element analysis is valid, and the fatigue inducing stress variations due to these types of load effects c
38、an be ignored. Also, for the particular method presented in Appendix 3, it is assumed that the short-term stress variation in a given sea-state is a random narrow-banded stationary process. Therefore, the short-term distribution of stress range can be represented by a Rayleigh distribution. The key
39、components of the Spectral-based Fatigue Analysis method for the selected structural locations can be categorized into the following components: Establish fatigue demand Determine fatigue strength or capacity Calculate fatigue damage or expected life These analysis components can be expanded into ad
40、ditional topics, as follows, which become the subject of particular Sections in the remainder of this Guide. The topic, “Establish Fatigue Demand”, is covered in Sections 2 through 7. The topics of “Determine Fatigue Strength or Capacity” and “Calculate Fatigue Damage or Expected Life” are the subje
41、cts of Sections 8 and 9, respectively. Reference can be made to Section 1, Figure 1 for a schematic representation of the Spectral-based Fatigue Analysis Procedure. Section 1 Introduction ABSGUIDANCE NOTES ON SPECTRAL-BASED FATIGUE ANALYSIS FOR VESSELS .2004 3 A purposeful effort is made in this Gui
42、de to avoid complicated formulations, which will detract from the concepts being presented. The most complex formulations are those relating to the calculation of fatigue damage resulting from the predicted stress range. These formulations are presented in Appendix 3 of this Guide. It is often at th
43、is formulation level that valid variations of a method may be introduced, and for that reason, it is emphasized that the contents of Appendix 3 are provided primarily to illustrate principle, rather than as mandatory parts of the Spectral-based Fatigue method. Section 1 Introduction 4 ABSGUIDANCE NO
44、TES ON SPECTRAL-BASED FATIGUE ANALYSIS FOR VESSELS .2004 FIGURE 1 Schematic Spectral-based Fatigue Analysis Procedure (For Each Location or Structural Detail)Determine Still-w aterLoads and CheckEquilibriumSee 4/3Perform Analysis ofVessel Motion andWave-Induced LoadsSection 4ObtainEnvironmental Data
45、Section 3Establish FatigueDemandSections 2 thru 7EstablishFatigue StrengthSection 8ApplyRequired Safety FactorsDo for eachBase VesselLoad ConditionSee 2/5For each Heading Angle and Wave Freq.See 2/3Calculate RAOs for -y External Hydrodynamic Pressurey Internal Tank and Hold Loadsy Accelerations of D
46、iscrete MassesSection 5Assemble Load Cases for StructuralAnalysis and Check Dynamic EquilibriumSection 6Perform Structural Analysis to ObtainStress Range Transfer FunctionSection 7Calculate Fatigue DamageSection 9Calculate combined Fatigue Damagefrom Multiple Base Vessel Load CasesSee 2/7COMPAREExpe
47、cted StrengthTo Be Gre ate rThan or Equal toExpected DamageABSGUIDANCE NOTES ON SPECTRAL-BASED FATIGUE ANALYSIS FOR VESSELS .2004 5 Section 2: Establishing Fatigue Demand SECTION 2 Establishing Fatigue Demand 1 Introduction Sections 2 through 7 address the procedures used to estimate the fatigue dem
48、and at a structural location that is the object of the fatigue strength evaluation. 3 Stress Range Transfer Function (1 December 2007) With ocean waves considered the main source of fatigue demand, the fundamental task of a spectral fatigue analysis is the determination of the stress range transfer
49、function, H(|), which expresses the relationship between the stress at a particular structural location and wave frequency () and wave heading (). It is preferred that a structural analysis be carried out at each frequency, heading angle and “Base Vessel Loading Condition” (see Subsection 2/5) employed in the spectral analysis and that the resulting stresses are used to directly generate the stress transfer function. Normally, the frequency range to be used is 0.2 to 1.80 radians/second in increments not larger than 0.1 rad/s.
